package com.xk._01基础篇._03链表;

/**
 * @description: 动态数组 有动态缩容操作
 * @author: xu
 * @date: 2022/9/14 19:14
 */
@SuppressWarnings("unchecked")
public class ArrayList<E> extends AbstractList<E> {
    /**
     * 所有的元素
     */
    private E[] elements;

    private static final int DEFAULT_CAPACITY = 10;

    public ArrayList(int capacity){
        capacity = Math.max(capacity, DEFAULT_CAPACITY);
        elements = (E[]) new Object[capacity];
    }

    public ArrayList(){
        this(DEFAULT_CAPACITY);
    }

    /**
     * 清除所有元素
     */
    public void clear() {
        for (int i = 0; i < size; i++) {
            elements[i] = null;
        }
        size = 0;
        if (elements != null && (elements.length >> 1) > DEFAULT_CAPACITY){
            elements = (E[]) new Object[DEFAULT_CAPACITY];
        }
    }

    /**
     * 获取index位置的元素
     *
     * 时间复杂度：O(1)
     * 空间复杂度：O(1)
     */
    public E get(int index) {
        rangeCheck(index);
        return elements[index];
    }

    /**
     * 设置index位置的元素
     * @param index
     * @param element
     * @return 原来的元素ֵ
     */
    public E set(int index, E element) {
        rangeCheck(index);
        E old = elements[index];
        elements[index] = element;
        return old;
    }

    /**
     * 在index位置插入一个元素
     * @param index
     * @param element
     */
    public void add(int index, E element) {
        rangeCheckForAdd(index);
        ensureCapacity(size + 1);

        for (int i = size; i > index; i--) {
            elements[i] = elements[i-1];
        }
        elements[index] = element;
        size++;
    }

    /**
     * 删除index位置的元素
     * @param index
     * @return
     */
    public E remove(int index) {
        rangeCheck(index);
        E old = elements[index];
        for (int i = index + 1; i < size; i++) {
            elements[i-1] = elements[i];
        }
        elements[--size] = null;
        trim();
        return old;
    }

    /**
     * 查看元素的索引
     * @param element
     * @return
     */
    public int indexOf(E element) {
        if (element == null){
            for (int i = 0; i < size; i++) {
                if (elements[i] == null){
                    return i;
                }
            }
        } else {
            for (int i = 0; i < size; i++) {
                if (element.equals(elements[i])){
                    return i;
                }
            }
        }
        return ELEMENT_NOT_FOUND;
    }

    /**
     * 保证要有capacity的容量
     * @param capacity
     */
    private void ensureCapacity(int capacity) {
        int oldCapacity = elements.length;
        if (oldCapacity >= capacity) return;
        //新容量为旧容量的1.5倍
        int newCapacity = oldCapacity + (oldCapacity >> 1);
        E[] newElements = (E[]) new Object[newCapacity];
        for (int i = 0; i < size; i++) {
            newElements[i] = elements[i];
        }
        elements = newElements;
    }

    /**
     * 裁剪操作
     * 剩余空间占总容量的一半以上时，进行缩容
     */
    private void trim() {
        int capacity = elements.length;//当前容量
        int newCapacity = capacity >> 1;
        if (size >= (newCapacity) || capacity <= DEFAULT_CAPACITY){
            return;
        }
        // 剩余空间还有很多
        E[] newElements = (E[]) new Object[newCapacity];
        for (int i = 0; i < size; i++) {
            newElements[i] = elements[i];
        }
        elements = newElements;

        System.out.println(capacity + "容量大小缩容为" + newCapacity );
    }

    @Override
    public String toString() {
        StringBuilder string = new StringBuilder();
        string.append("size=").append(size).append(", [");
        for (int i = 0; i < size; i++) {
            if (i != 0){
                string.append(", ");
            }
            string.append(elements[i]);
        }
        string.append("]");
        return string.toString();
    }
}